Ultra short wave transmitting tube



Nov. 28, 1950 o. DOEHLER ETAL ULTRA SHORT WAVE mmsmmnm TUBE Filed Feb. 12. 1949 JEN 7 RLER N E Wf T L J aya 0% 33 Patented Nov. 28, 1950 ULTRA SHORT WAVE TRANSMITTING TUBE Oskar Doehler, Werner Kleen, and Harry Huber, Paris, France, assignors to Compagnie Generale dc Telegraphic Sans Fil, a corporation of France Application February 12, 1949, Serial No. 76,082

7 Claims.

The present invention has for its object an improvement in tubes intended for transmitting ultra-short waves, of the travelling wave type, the purpose of said improvement being to increase the amplification gain and the efliciency of such tubes.

The features of this type of tubes have already been described in co-pending patent applications Serial No. 794,164, filed on December 2'], 1947, and now U. S. Patent No. 2,511,407, granted June 13, 1950, and Serial No. 23,063, filed on April 1948, both relating to tubes or which the present invention is an improvement. 1

A tube of this type comprises an electron emitting source, a central electrode located inside a cylindrical anode along the axi thereof, said central electrode being raised to a negative potential with respect to said anode and thus performing the function of a cathode. The anode is adapted to form a delay line provided with an input terminal and an output terminal, A magnetic field is applied to the inside of the tube, in the direction of the axis of the cathode, and an ultrashort wave is fed to the input terminal of the delay line. During the operation of the tube, the electrons move through the space between the 2 and B the value of the magnetic induction, If a D. C. voltage U is applied between the anode and the cathode and if d is the distance between the two electrodes, the electric field E in the space between said electrodes will be of the value:

According to Formula III, the speed of the electrons, Ve, is independent of their distance from the cathode, said distance called at being cathode and the delay line and give up their energy to the wave fiowing through said line. Under these conditions, the power obtained at the output terminal of the delay line is greater than the power which was applied to the input terminal; the tube therefore behaves as an amplifier. Any feed-back that may be liable to cause self-oscillation of the tube is prevented by means of suitable screens and breaks in the path.

For the energy exchange between the electrons and the Wave to be effected under the most eflicient conditions, it is necessary for the electrons to travel round the cathode at the same speed as the wave, the speed of propagation of which depends on the properties of the delay line.

Since the cathode is usually of fairly large diameter and the ratio between the radii of the two concentric electrodes is nearly equal to 1, calculations may be made as though the anode and the cathode were located in two parallel planes. Under these conditions and neglecting the influence of the space charge between the electrodes, the speed Ve of the electrons can be calculated from the formula:

neg 1) wherein E is the intensity of the electric field in the space between the anode and the cathodes reckoned from the cathode. It would thus be possible to obtain equality of speeds between the wave and the electrons. But a more thorough study shows that precisely the space charge, which had been neglected during the foregoing calculations, plays an important part. As a rough approximation it may be admitted, if account is taken of said space charge, that the speed Ve of the electrons is determined by the equation:

U :1; dB d (W) In reality, this speed is in practice between the limit values defined by Equations III and IV. The exact law of variation of said speed, which cannot be stated with certainty, depends on the characteristics of the tube used. In any case, Va is a function of the distance as between the electron and the cathode, which means that equality of speeds between the wave and the electrons can be obtained, by acting on the parameters U and B, only for one value of 1:, said value being a function of said parameters. During the operation of the tube, owing to the transfer of energy from the electrons to the anode, the electrons move closer to the anode and consequently move away from the cathode during their travel around the same. Therefore m varies and, according to Equation IV, Ve also varies, so that, if equality of speeds between the wave and the electrons has been obtained near the input terminal of the anode, the speed of said electrons, which have not yet given up a substantial part of their energy, will vary throughout the entire length of their. path and equality of speeds will not be obtained. COIL" sequently the amplification gain and the efflen r o .the a d ga sed.- j

The present invention has for its object to decrease or even prevent this objectionable effect. Although the law of variation of the speed Ve as a function of a: is not eXactly known, it can be deduced from the formulae hereinbefore given that Ve must certainly increase with a: and it may be admitted that owing to the fact that during the energy exchange, the amplitude of the wave progressively increases exponentially, the distance of the electrons from the cathode also increases exponentially. Consequently, equality of speeds between the wave and the electrons throughout the path of the electrons can be at least approximately obtained, if the speed of propagation of the wave also increases. According to the invention, in combination with the tube hereinbefore defined, the delay line is so constructed that the wave is accelerated from the input terminal to the output terminal of said line. This acceleration is preferably obtained by gradually decreasing the longitudinal inductance of the delay line along said line. If use is made by way of a non-limitative example of a delay line of the shape of a flattened helix,

or which is formed by a wire which is bent double and curved concentrically to the cathode, this result is obtained by giving to said helix a variable pitch that increases from the input terminal to the output terminal. Assuming as hereinbefore mentioned that the distance of the electrons from the cathode increases exponentially, and consequently that their speed Ve also increases according to .Formula IV, it will be understood that, in order to obtain a maximum transfer of the power, it is necessary also to increase the speed of the wave exponentially so as to maintain the equality of the two speeds. This is effected by increasing the pitch p of the helix accordin to the equation:

wherein y is the length of the path of the electrons measured from the input terminals of the amplifying system, or being a coeiiicient which is dependent on the input amplitude, the dimensions of the tube and the D. C. voltage; on the other hand, a is greater as the high-frequency voltages at the output of the tube are higher. For high power, the variation of p as a function of y is very great, of the order of magnitude of 1 to 2,. and considerably affects the operation of the tube. It will moreover be observed that, for a given value of or, the tube can be made to operate at different power levels while maintaining the most favorable conditions of operation by giving suitable values to the parameters U and B.

The invention will be more clearly understood by means of the accompanying figures which show, by way of a non-limitative example, one embodiment thereof.

Fig. 1 shows a plan view of a tube according to the invention.

Fig. 2 shows a section of said tube along the plane aa.

Fig. 1 shows the cathode provided at K with the electron emitting portion, the delay line H which also acts as the anode and through which a travelling Wave fiows from the input terminalI to the output terminal 0. The anode is raised to a positive potential with respect to the cathode C, thereby producing a radial electric field E. A magnetic field B, supplied by the poles NS shown in Fig. 2, is applied parallel to the axis of the cathode and therefore atright angles to the plane of the figure. The polarity of said field is determined by the direction of the wave propagation. At P is mounted a screen that prevents the electrons which have followed the trajectory between the terminals I and 0 from returning opposite the input terminal I and setting up self-oscillation. The helix H, according to the invention is of a pitch p which increases from the input terminal to the output terminal of the tube. All these elements are arranged inside the enclosure T.

Fig. 2 shows a section of the tube of Fig. 1 along the line (1-11. It shows the cathode C, the delay line H of the shape of a flattened helix, said helix being held by supports A comprising rings of ceramic material arranged coaxially to the cathode. Said supports serve at the same time for holding the cathode C and the whole arrangement is mounted inside the enclosure T.

In this example, the source of electron K is shown as forming part of the central cathode. It is possible to devise other designs according to which the emitting element is independent of said cathode and may, in particular, be located adjacent the input terminal, in the space between the cathode and the delay line, as provided in the aforesaid co-pending application Serial No. 794,164, filed on December 27, 1947.

The invention is not limited to amplifying tubes, but also covers oscillator tubes. For that purpose it is necessary to provide a back-coupling between the input and output circuits and arrange an oscillating circuit therein. The invention covers in general any tube in which a magnetic field is provided at right angles to the direction of emission of the electrons, and which is provided with an input terminal and an output terminal, and in which the amplification is obtained by means of an exchange of energy between the electrons and a wave which is fed to the input terminal and the speed of propagation of which is approximately equal to the speed of the electrons.

What we claim is:

1. In an electronic discharge device having an emissive cathode, means for establishing a substantially time-constant magnetic field, the electron current of said cathode being located within sad field, the lines of force of the field, in a given direction, being substantially parallel to the surface of the said cathode, and an interaction duct comprising two spaced substantially parallel conductors having their surfaces parallel to the lines of force of the magnetic field, terminal connections to the cathode and to both conductors enabling the surface of the cathode to be brought to a predetermined potential and the production between the conductors of a transverse electrical field substantially perpendicular to the magnetic field, at least one of the conductors comprising elements constitutinga delay line and having an input terminal and an output terminal for ultrahigh frequency and means for progressively increasing the propagation speed of energy in the line in the direction of electron current propagation.

2. A device as in claim 1, wherein the propagation speed of energy in the line is increased exponentially.

3. A device as in claim 1, wherein the delay line has a gradually decreasing coefiicient of self induction from the input terminal toward the output terminal.

4. A device as in claim 1, wherein the delay line has a coefficient of self induction decreasing exponentially from the input terminal toward the output terminal.

5. A device as in claim 1, wherein the delay line has the shape of a helix of gradually increasing pitch from the input terminal toward the output terminal.

6. A device as in claim 1, wherein the delay line has the shape of a helix having a pitch increasing exponentially from the input terminal toward the output terminal.

7. An electronic discharge device comprising an emissive cathode, means for establishing a substantially time-constant magnetic field, an interaction duct comp-rising two substantially parallel conductors having their surfaces parallel to the lines of force of the magnetic field, one of the conductors being recessed, the cathode being situated in the recess of said recessed conductor with the emissive surface thereof registering with the surface of the said recessed conductor, the lines of force of the magnetic field, in a given direction, being substantially parallel to the emissive surface of the said cathode, terminal connections to the conductors thereby to produce therebetween an electrical potential givin rise to a substantially time-constant electrostatic field substantially perpendicular to the said time-constant magnetic field, at least one of the conductors including elements forming an electrical delay line, thereby to produce a radio-frequency field having an electrical component perpendicular to the crossed substantially time-constant electrostatic and magnetic fields, said elements having the characteristics of longitudinal inductances inserted in a Lecher line, and being so dimensioned that the phase propagation velocity along the delay line is less than in space and substantially equal to the velocity of electrons in the duct, the said electron velocity being determined by the ratio of the intensities of the electric and magnetic fields, the said conductors, from the point of view of radio-frequency waves travelling over the surface thereof, having input and output extremities separated from each other to enable mutual decoupling thereof and prevent feed-back oscillations, the said extremities being provided with means for coupling to outside circuits for exciting an electromagnetic wave in the radio frequency input terminal and for collecting amplified energy at the radio-frequency output terminal. 7

DOEHLER, OSKAR.

KLEEN, WERNER.

HUBER, HARRY.

REFERENCES CITED lhe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,064,469 Haeff Dec. 15, 1936 2,289,756 Clavier et a1. July 14, 1942 2,300,052 Lindenblad Oct. 27, 1942 

